1. Field of the Invention
This invention generally relates to cameras in which the film is completely unwound from its receptacle prior to use. Specifically, this invention relates to relatively low-priced, manually operated cameras in which the film is prewound. In particular, this invention relates to a camera having a film interlock mechanmism for preventing a user from rewinding unused film into its receptacle before the film is completely unwound.
2. Description of the Related
There have been many different types of low-priced, manually operated film advance mechanisms in recent years. This has been a result of the expanding market and technical development of disposable cameras.
However, the very characteristics that afford such cameras to be low priced and hence disposable also yield certain disadvantages. One such drawback is that disposable cameras are preloaded with film having a limited shelf life. The shelf life of the film is approximately 1.5 years. If the film in the disposable camera is not used before this period of time elapses, the pictures taken from this film will be of substandard quality.
Another disadvantage of disposable cameras generally, is the very fact of their disposability. Although discarding after a single use may be advantageous to some consumers, environmental degradation and a waste of non-renewable natural resources is a concomitant result.
A further disadvantage of some prewind cameras, and some other manually operated permanent cameras as well, is after some pictures have been taken, if the film access door is accidentally opened, the exposed film is mined by having light exposed thereon. To avoid such accidents, after film loading, many cameras now fully unwind the unexposed film from its lightproof casing onto the receiving spool in the opposite chamber. Then, after each picture is taken, the exposed frame is backed onto its lightproof casing. When this procedure is utilized, if the film access door is accidentally opened, only unused, that is, unexposed film, is ruined and the exposed film having the pictures taken by being already backed into its casing is safely protected in its lightproof casing. An unfortunate side effect of this procedure, when it is manually operated, is that often the camera operator does not know what type of camera he is using, a conventional shoot-and-unwind camera, or a prewind camera that rewinds after each shot. If a consumer thinks he is using the former but instead is using the latter, upon loading the film, after the first picture shot, he will advance the film, that is, he will rewind the film back into the film casing, unable to be retrieved or used in its entirety. There is therefore a great need in the art for providing a feature on the camera for preventing this type of accident from occurring.